I think it’s mucho , or the first one
The answer is “somos”. I got this answer because Elena y yo is like saying we, and we know that “nosotros” is we in English, so you would conjugate “ser” into the “nosotros” version “somos”.
18mandas una tarjeta a un amigo? (Yo envío una tarjeta a un amigo?). 19 ( haces la tarea para tu profesora? Yo hago la tarea para la profesorado